1. Field of the Invention
The present invention relates to concrete improved to have raised workability.
2. Description of the Related Art
Generally, in order to obtain concrete having high strength, water-cement ratio should be as small as possible (Hereinafter xe2x80x9cwater-cement ratioxe2x80x9d and xe2x80x9cwater-powder ratioxe2x80x9d which is used in case of mixing an admixture such as blast furnace slag fine powder, limestone fine powder, or silica fume, etc. in addition to cement, have the same meaning.). On the other hand, it is important that fresh concrete shows sufficient fluidity from a construction side in order to secure suitable workability.
However, in case that cement is a single component used as a fine particle material which constitutes concrete, if the water cement ratio becomes about 35% or less, the fluidity of concrete becomes very poor and it is difficult to secure satisfactory workability. Especially, the super high strength concrete having a design strength of 600 kgf/cm2 class established in connection with high rising of a building, in other words, in case that waiter-cement ratio becomes about 25%, it has been a big problem to ensure the workability.
In order to solve the above problem, recently, a method of mixing comparatively large amount of blast furnace slag fine powder or limestone fine powder having a mean particle diameter of 1-3 micrometers, or silica fume having the mean particle diameter of 0.1-0.3 micrometers with cement is adopted. This method is based on an idea of filling up gaps among cement particles usually having the mean particle diameter of about 15 micrometers by supplying particles having the mean particle diameter of about 1-3 micrometers or particles having the mean particle diameter of about 0.1-0.3 micrometers, thereby simultaneously reducing frictional resistance among cement particles and frictional resistance between fine particles and aggregate, and, as a result, raising the fluidity of concrete and securing workability.
According to this method, the blast furnace slag fine powder, limestone fine powder, and silica fume which consist of a very fine particle compared with a cement particle are mixed, while remaining as fine particle, with other compounding ingredients at the time of kneading concrete. However, such fine particles having the mean particle diameter of 1-3 micrometers or less which consist of fine powder easily cause secondary aggregation in a powder state to form coarse powder, namely, have a tendency to form coarse particles. Accordingly, these particles, even though each particle is fine, cause secondary aggregation to form coarse powder which cannot sufficiently fill up gaps among cement particles when they are mixed with cement. As a result, there is a defect that an improvement in fluidity is not sufficient. This is one of the reasons to use comparatively large amount of such fine powder.
Moreover, since the particle diameter of the blast furnace slag particle or the limestone particle obtained in a usual dry type pulverization process using the ball mill or roll mill is around 15 micrometers, it is necessary to use a special pulverizer for producing the blast furnace slag fine powder or the limestone fine powder having the mean particle diameter of 1-3 micrometers or to employ complicate milling process. To obtain such fine power is not only troublesome but causes a problem of producing expensive material because of high production cost. Because of the above problem, when such fine powder is used so much as admixtures of concrete, it becomes disadvantageous in respect of cost, and it is difficult to put such a method to practical use. Further, silica fume has a similar problem because expensive product imported from overseas is used.
Therefore, a method which can increase the fluidity of concrete more effectively than the conventional method using the above mentioned blast furnace slag fine powder or limestone fine powder in dried condition, and simultaneously, produce easily such powder is expected. The object of the present invention is to increase the fluidity of concrete more effectively by using limestone powder and to provide improved concrete having solved the above problem by supplying limestone powder used in concrete comparatively simple method.
As a result of research to solve the above problems, the inventors have found;
(1) without using a special pulverizer or complicate pulverizing process, but employing wet milling method which can mill limestone into fine powder, the particles of ground calcium carbonate obtained from the limestone and having the mean particle diameter of 0.5-3 micrometers exist in such condition that each particle is dispersed without causing the above-mentioned secondary aggregation in an aqueous slurry thereof. Therefore, by using only comparatively small amount of this slurry as an admixture or a powder material of the concrete, each particle fills easily into gaps among cement particles and gaps among paticles of cement and aggregate. As a result of ground calium carbonate particles filling up sufficiently these gaps, frictional resistance between cement particles and that of cement particle and aggregate are remarkably reduced and the fluidity of the concrete is increased, and
(2) when silca fume consisting of silica particles having the mean particle diameter of 0.1-0.3 micrometer is used in addition to the aqueous slurry of above-mentioned ground calcium carbonate, since this silica particle is more fine than ground calcium carbonate particle, it further goes into gaps among cement particles, gaps between cement particle and aggregate, and gaps among cement particle, ground calcium carbonate particle and aggregate thereby futher being able to fill up these gaps. As a result, frictional resistance between cement particles and that of cement particle and aggregate and frictional resistance among cement particle, ground calcium carbonate and aggregate are remarkably reduced and the fluidity of the concrete is increased.
The present invention was achieved based on the above finding and relates to:
1. Concrete characterized by containing aqueous slurry of ground calcium carbonate having the mean particle diafmeter of 0.5-3 micrometers produced by wet pulverization of the limestone, and
2. Concrete characterized by containing aqueous slurry of ground calcium carbonate having the mean particle diameter of 0.5-3 micrometers produced by wet pulverization of the limestone and silica fume which comprises silica particles having the mean part diameter of 0.1-0.3 micrometers.